Cooked rice which is a staple food in the countries of East Asia is so-called "steamed and boiled rice. " It is cooked by a time-consuming procedure which comprises the steps of first washing raw rice (which means hulled rice in the instant specification and claims) with water, allowing the washed rice to absorb water amply and thereafter steaming and boiling the water-impregnated rice for a long time. Ample impregnation with water and an appropriate extent of boiling and steaming are required for preparing the cooked rice of soft texture and agreeable teeth-resistance. The requirement for rigid control of these conditions prevents quick cooking. The fact that this cooking consumes much time also constitutes one disadvantage.
Another typical example of cooked rice is pilaf. This is prepared by frying washed rice with oil, whereafter the fried rice is steamed and boiled in the presence of added water. It has the disadvantage that the texture is generally hard. This disadvantage can be overcome by continuing the treatment of steaming and boiling for a relatively long time. Nevertheless, it still has a drawback in that the cooking consumes much time. In view of the above, there is a need for development of fast cooking rice which readily provides cooked rice of the class described above.
What is called "gelatinized rice" has heretofore been regarded as a kind of fast cooking rice. This is usually prepared by subjecting the rice to the ordinary treatment of steaming and boiling for thereby gelatinizing the rice starch and thereafter drying the starch-gelatinized rice. By mere addition of hot water at a temperature of about 80.degree. C or over, however, the fast cooking rice prepared as described above fails to reconstitute itself into cooked rice possessed of the desired texture. It is not converted into desirable cooked rice unless it is boiled for several minutes by heating. Such time-consuming treatment does not befit the fast cooking rice for which instantaneousness counts strongly.
There is Japanese Patent Publication No. 1581/1958 which employs substances similar to those used in the present invention for treating rice grains. But, this publication aims to prepare highly nutritious rice grains by coating raw rice grains with sodium alginate, cow's milk and powdered milk. As this rice grain is quite raw, it requires the ordinary treatment of steaming and boiling for providing a cooked rice. Therefore, this prior art is obviously different from the present invention in the object and the product to be prepared.
A method which produces cooked rice by mere addition of hot water has been disclosed by Japanese Patent Publication No. 5729/1959. The method disclosed therin comprises first steaming and boiling the raw rice to a extent mild enough to pregelatinize the surface layer of the rice grains, then causing the steamed and boiled rice to absorb a paste such as dextrin or sodium carboxymethyl cellulose, subjecting the treated rice to a treatment for regular steaming and boiling for thereby completely gelatinizing the rice grains to the inside center and finally drying the gelatinized rice. The fast cooking rice which is obtained by this method has the disadvantage that, when hot water is added thereto immediately before its consumption, the required reconstitution takes much time or the reconstituted rice has a rather hard texture, possibly because the rice, in the final treatment of drying, suffers partial retrogradation of the rice starch which has once been gelatinized. Furthermore, the process of manufacture is complicated.
Studies have also been continued with a view to producing fast cooking rice which can be reconstituted into as exact an equivalent of regular boiled and steamed rice as practicable. For example, there is a method which utilizes puffed rice, with due consideration of the fact that gelatinized rice is obtained by puffing rice grains. If simply puffed rice is used as a fast cooking rice, it is quickly softened in the presence of hot water added thereto prior to its consumption. Nevertheless, it has the disadvantage that the hot water deprives the rice grains of their shape and renders them quite different from regular boiled and steamed rice in taste, texture, viscoelasticity, etc. Japanese Patent Publication No. 27700/1971 discloses a method which comprises the steps of first puffing raw rice to a slight extent, then immersing the puffed rice in water for thereby heightening the water content thereof, subsequently gelatinizing the puffed rice of increased water content, thereafter drying the gelatinized rice until the water content thereof decreases to a prescribed level and finally re-puffing the dried rice. The fast cooking rice produced by this method, however, suffers from an undesirable spongy texture and poor teeth-resistance. It has the further disadvantages that the process for manufacture is complicated and the yield is consequently low.
As described above, there have been conceived methods for the manufacture of fast cooking rice which combine the treatment of puffing with other treatments. These conventional methods, however, are complicated from the operational point of view because the water content of rice grains must be rigidly regulated in the course of treatments and consequently because the rigid regulation of water content calls for additional treatments, and so on. Methods which involve use of oil and fat are not desirable because the oil and fat incorporated into the rice grains degrade the taste and induce oxidation of itself to the extent of heavily impairing the quality of fast cooking rice. Also the removal of excess oil and fat in the course of manufacture demands much time and labor.